Air pollution is caused by the following _________: about half of the problem is caused by vehicles.
With the ____________ (develop) of industry, air pollution is getting more and more serious.
We don’t have to take great pains to control waste, but action and a grateful heart are needed; thank the water that runs through our fingers, and save it for poor Arabian or African countries struggling in water ______ (short);
I'll stop and take a deep ____.
“Learn through use” is a good piece of ________ (advise) for those who are studying a new language.
I would persuade her to make room for you ______it be necessary.
A. could B. might
C. should D. would
